Klopp's fitness woes are currently so severe that he was forced to field left-back Jose Enrique -- who had previously been frozen out of the first-team set-up -- in the centre of defence in Friday's 2-2 draw at Exeter City in the third round of the FA Cup.

Caulker has been on loan from Championship club QPR at Premier League side Southampton this season, but has so far made just eight appearances for the St Mary's side.

After QPR also dropped down to the Championship last season, Caulker moved to Southampton in a bid to restore his Premier League career and add to the one senior England cap he earned in 2012.

Caulker came through the youth ranks at Tottenham but only made 17 Premier League starts for Spurs amid loan spells in the lower leagues at Yeovil Town, Bristol City and Swansea City, playing his part in the latter club's first Premier League campaign under Rodgers' management in the 2011-12 season.

Cardiff signed him for £8m for in 2013 and he was ever-present in their one and only Premier League campaign, scoring five goals. Last term, he missed just three league matches for QPR.